Shafts thru the transom?

[Frosty]

I made it myself. The shaft tube is a localy purchased shaft tube with a stuffing box on the inside but not what you would immagine, The stuffing box is another 12inches inside of the transom with a stainless steel threaded tub inbetween the two. Ille get my mate around again with the digital camera. The shaft is 4 foot in total length and is 2 inch dia. I changed the stuffing box for a deep sea seal that I had made up. Its just a bronze bush with with an oil seal at both ends and is supplyed with an oil supply this has been very succesfull. Before I did this I would blow out bits of greasy rope in an hour.I used to grease the shaft tube but now i dont so as to get water up the shaft and cool the seals wich could get very hot. I have pressure fed the shaft with sea water from a pick up at the side and drilled into the shaft tube. It might be a good idea to drill another nipple up at the top on the inside for water out ,then there would be an exchange of water. I might do that one day but up till now I have had no problems. Now if you want talk Rudders thats a different storey

[Hydro]

Capttpan.
We manufacture a similar drive see post number 93 on this thread

[Steve H]

Very impressive fuel economy for such a heavy boat. What kind of range do have?

Steve Hixson

[Frosty]

I can carry 1600 liters in 2 tanks, one in each hull. I have also 600 liters of water.So theres 2 tons already. The boat is a Seawind made in aus. this is thier new power boat range called the ventura mine is the 44 foot , the largest that they do. The production boat wieghs in at 12 I think, -but that must be a dry wieght. I took a very great deal of care in the fit out wich was done in Phuket Thailand. Hand made in a wood called My yom hom, a very light wood and redish in colour. It took one year to compete. Wieght is a killer for cats. Im not exactly sure on the fuel consumption its not over 50 and its not below 40. I would really like some fuel flow meters but a proper kit by flo-scan is expensive. I log fuel on every trip so I know it in those figures.

[Ragman]

Hi Jack
I read with great interest your search for you cat and your solutions in terms of Hull, engine and that fantastic "surface props". Any chance you can post some more pics of your boat. How is the preformance of your latest fine tuning. I am on this journey myself.

Smooth seas always mate

[Frosty]

Hello Ragman
I am not far from Singapore--Langkawi. I do not at the moment have a digital camera, I had to get a friend to take some photo;s BUT i am thinking buying a new telephone next week with a built in camera. I am inetersted in what you are doing.Have you bought the hull? Tell me what you are doing and what you are up to!!
As far as my fine tuning is concerned i can get her up to 24 knots and at 14 tons with 500hp I think I am doing well and dont expect any more. The only further fine tuning that I would like to do is is increase the dia of the props by 1 inch. this I thought would bring the slip down a bit. Its more than 20% at the moment and I am not sure if thats acceptable with those props?

[Ragman]

Hi Jack

Thanks for replying my email. We are quite close, it seems. No i haven't brought my hull yet. I am at the stage of looking at a new cat maybe 3-4 yrs from now. So i am in the learning stage. I would be most grateful for any tips that you can give me. Your shaft systems look really good with the cupping prop form NZ. Can i trouble you for some pics and specs of your boats. I went to look at the Oz site where you got your hull but seem to have found the wrong one.

Cheers
Ragman

[tom kane]

Originally Posted by jack frost

I made it myself. The shaft tube is a localy purchased shaft tube with a stuffing box on the inside but not what you would immagine, The stuffing box is another 12inches inside of the transom with a stainless steel threaded tub inbetween the two. Ille get my mate around again with the digital camera. The shaft is 4 foot in total length and is 2 inch dia. I changed the stuffing box for a deep sea seal that I had made up. Its just a bronze bush with with an oil seal at both ends and is supplyed with an oil supply this has been very succesfull. Before I did this I would blow out bits of greasy rope in an hour.I used to grease the shaft tube but now i dont so as to get water up the shaft and cool the seals wich could get very hot. I have pressure fed the shaft with sea water from a pick up at the side and drilled into the shaft tube. It might be a good idea to drill another nipple up at the top on the inside for water out ,then there would be an exchange of water. I might do that one day but up till now I have had no problems. Now if you want talk Rudders thats a different storey

A talk about rudders relating to surface drive would be very interesting and enlightening to many of us I am sure.

[Frosty]

hello Tom
Well where to start i am not an expert but have just battled my way through to rudders that seem to work well. Arneson of course dont have rudder and move the entire shaft( by the way I saw once a pair of arnesons that had lost its steering fluid and the 2 shafts touched oooohh what a mess, should have had a mechanical tie bar)
Any way i use the tunnel rudder which according to sony levy, (who I actually know personally) says in his book that this is the most efficient way to steer a suface propellor.

[tom kane]

Thanks jack frost.Perhaps we will be able to discuss rudders RE.Surface Drive some where soon,some one said they were going to start a thread and had good ideas.I have tried most ideas known and some probably not known which can give 50 degrees of steering,and turn a boat in its own length at idle and eliminate most of the parsitic drag.I have not had a lot of success with some type of tunnel rudders,but have used a narrow tunnel rudder behind the prop,with good success.

[Frosty]

Tom
I have only experimented with the tunnels, more of fine tuning really, which all of my mods had no effect. The problem i had with the tunnels is getting strength down the blade. In a normal blade rudder the shaft can travel the depth of the blade but the tunnel does not, so I had trouble keeping a nice slim efficient blade and in parallel of course.
The reason i had no effect on the rudder modifications was that the problem was not the rudders but a carelessy fitted pair of bulbous bows. I pondered over this steering problem for months untill i read some thing on the web about how bulbous bows on small boats were fashion rather than a nessecity. After great thought and planning i modified the bulbous bows. Cured high speed steering wander immediately and put a knot on top. Those bulbous bows are a funny thing. Now theres another story.
Oh by the way I have asked on this forum about how parallell the rudders should be. i have had no reply. At present i set them up absalutely Parallell but I have read that you would'nt do that on a pair of Mercruisers, so I dont know if I should have a bit of toe in or toe out. Ive tried abit of this and that but not come to any conclusion.

[tom kane]

This is one of many steering systems tried.Twin rudders on a drive shaft that can be run horizontal to the keel or down 20 degrees or more.Surface Drive or subsurface drive.Rudders will turn flat to transom and block the flow of water from prop in forward or reverse,boat turns by propwalk in it`s own length.Droping the drive down gives more reaction.Hull form dictates performance.Fitting trimable tabs on rudders gives better steering,about 40 degrees.Rudders give about 28 -30 degrees of steering before a stall drag takes effect.A complete circle rudder,(a kort kozzle with out a venturie effect can give 50 degrees of steering and used on a surface drive when prop is 50 percent immersed should not create excessive drag.

[tom kane]

Originally Posted by Buck

Has anyone tried this? Maybe with struts on underside of swim platform W/ conventional trim tabs and rudders?

The image shows the slot in a hull,all that is needed to fit a CAM.A.PROPULSION PIVOTAL DRIVE.Surface Drive or SubSurface Drive and you can fit a jackable inboard/outboard drive if you want,or a transom mounted jet unit.Motor cn be in stern or amidships.

[tom kane]

Originally Posted by gonzo

Surface piercing props would not work behing a strut . The eddies formed by the strut would interfere with water flow. Look at the design of all surface drives; they have a streamlined bottom. A tunnel drive uses standard propellers and shafts. They are, however, tricky to design properly.

Just browsing through some of the older posts.The image shows a very fast boat with a big strut close to a surface piercing propeller,not at all like some surface propulsion units.

[Frosty]

I guess you got to have some thing holding the prop at those shaft lengths. But in any case above the prop is ok, because that bit is out of the water. Each swipe of the blade needs cean green water. Nothing has to be infront of the prop ,-- not even a skin fitting and especially a trim plate.
I dont look at them as a propellor as such more of a sculling device-- You know sculling when you wipe the blade of an oar backwards and forwards in the water twisting it for each swipe. I look at a surface prop more like that,--a rotating sculling devise!!! , its certainly not a screw.